Knowledge of large-scale mechanical properties is essential for estimating the stability of rock slopes being deformed by deep creep and especially for predicting a transition to rapid sliding. Standard geomechanical testing procedures may not result in significant values as the volume of the mass movements under consideration exceeds the volume of even the largest in situ tests by several orders of magnitude. Seismic measurements may help to estimate some of the relevant mechanical properties by direct correlation with the seismic velocities. However, not all parameters necessary for a stability analysis correlate closely with seismic velocities. An alternative approach could be the geomechanical modelling of the structures and properties of the creeping or sliding mass, as determined from seismic exploration. In this paper, we present an application of this approach to the giant landslide of Koefels. The development of the creeping rock mass, which represents the initial phase of the mass movement, has been successfully modelled by assuming a transition of the originally compact rock mass to "soft" rock, controlled by a Mohr-Coulomb and no tension yield criterion. Geomechanical parameters are determined by fitting the geomechanical model to the seismic results. An apparent angle of internal friction has been determined in the range 20-24 degrees. These low values are compatible with the fact that a transition to rapid sliding took place in the past. (C) 2001 Elsevier Science Ltd. All rights reserved.
